Numerous works of domestic and foreign authors are devoted to toxicology of pyrethroids, however the issues related to pathogenesis of an acute poisoning of animals with pesticides of that group as well as the principles of laboratory diagnostics at an early stage of intoxication and pathogenetic therapy at poisoning warrant further investigations. <...> For many years deltamethrin has been successfully used in plant growing as well as in animal husbandry creating a poisoning hazard in case of violation of treatment regulations. <...> Morbidity and clinical outcome depend largely on severity of functional endocrine and immune systems disorders. <...> The purpose of the study was to determine dynamics of adaptive and compensatory reactions in animals at an early stage of an acute intoxication with deltamethrin. <...> In experiment white laboratory rats as an established mammal model in biomedical research were used. <...> The experiment was performed on male rats (weight of 180-200 gr) arranged in 6 groups (of 10-12 rats each). <...> Animals from groups II, IV and VI have been subjected to an acute peroral intoxication with deltamethrin (Butox 50, Intervet, Netherlands) in a dose of 43.5 mg/kg of body weight. <...> Glucose content was estimated in whole blood of rats, and concentration of insulin and corticosterone was assayed in blood serum. <...> Pieces of animal timus were fixed in 4 % neutral formaldehyde, dehydrated in alcohols with the increasing concentration and embedded into paraffin. <...> For identification of mast cells the histologic sections were stained with Bismarck brown to Shubich. <...> On day 3 after poisoning the blood concentration of corticosterone and glucose in rats remained high along with a decrease in insulin content. <...> Photomicrographs showed a reduction in the number of thymocytes, activation of apoptosis, an increase in quantity of mastocytes along with an intensification of degranulation as well as development of haemodynamic disorders in thymus when poisoning rats. <...> In a week after intoxication the thymocytes level was partially restored. <...> No animal died during experiment which evidences the efficiency of adaptation and compensatory mechanisms in experimental rats, including hypothalamic-pituitary thymic system. <...> Results of our researches make a contribution to understanding compensatory and adaptive mechanisms under experimental intoxication, and allow estimating functional capabilities of body systems when developing pharmacological correction at poisonings. <...> Keywords: pesticides, deltamethrin, corticosterone, insulin, glucose, thymus, rats, intoxication The global market for synthetic pyrethroids <...>